Method and apparatus for regenerating a NOx trap and a particulate trap

ABSTRACT

An apparatus comprises an emission abatement device and a ratio oscillator. The emission abatement device comprises a NOx trap and a particulate trap. The ratio oscillator is configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles. An associated method is disclosed.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to methods and apparatus fortreatment of emissions present in exhaust gas.

BACKGROUND OF THE DISCLOSURE

Emission abatement devices are used to treat emissions present inexhaust gas. For example, there are NOx traps and particulate traps. NOxtraps are used to trap oxides of nitrogen (i.e., NOx) and particulatetraps are used to trap particulate matter. From time to time, the NOxtraps and particulate traps are “regenerated” to purge them of thecomponents trapped thereby for further use of the traps.

SUMMARY OF THE DISCLOSURE

According to an aspect of the present disclosure, there is provided anapparatus comprising an emission abatement device and a ratiooscillator. The emission abatement device comprises a NOx trap and aparticulate trap. The ratio oscillator is configured to oscillate aratio of the oxygen content and regenerative agent content of a flowadvanced to the emission abatement device so as to alternately partiallyregenerate the NOx trap and the particulate trap for a plurality ofcycles. An associated method is disclosed.

The above and other features of the present disclosure will becomeapparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram showing an apparatus foroscillating injection of a regenerative agent into a flow of exhaust gasfor regeneration of a downstream NOx trap and particulate trap of anemission abatement device; and

FIG. 2 is an exemplary graph showing oscillation of a ratio of theoxygen content and regenerative agent content of the exhaust gas flowadvanced to the emission abatement device.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the disclosure to the particular formsdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives following within the spiritand scope of the invention as defined by the appended claims.

Referring to FIG. 1, there is shown an apparatus 10 for regenerating aNOx trap 12 and a particulate trap 14 of an emission abatement device16. The traps 12, 14 may be separate components as in option 1 of FIG. 1or may be portions of an integrated device as in option 2 of FIG. 1.

The apparatus 10 includes a ratio oscillator 18. The ratio oscillator 18is configured to oscillate a ratio of the oxygen content andregenerative agent content of a flow advanced to the emission abatementdevice 16 so as to alternately partially regenerate the NOx trap 12 andthe particulate trap 14 for a plurality of cycles until completion ofregeneration of the traps 12, 14. As such, a given quantity ofregenerative agent is used to regenerate both the NOx trap 12 and theparticulate trap 14. Performance of such “double duty” by a givenquantity of regenerative agent reduces overall consumption of theregenerative agent. In addition, by dividing regeneration of theparticulate trap 14 into a plurality of events, a potentially damagingincrease in the temperature of the particulate trap 14 is avoided.

The ratio oscillator 18 oscillates the ratio of the flow advanced to theemission abatement device 16 between higher and lower agent levels(e.g., between relatively agent-rich and relatively agent-lean levels).The NOx trap 12 is partially regenerated with the regenerative agenteach time that the ratio is at a higher agent level. In addition, anoxidation catalyst 19 (“OC”), such as a diesel oxidation catalyst,upstream from or integrated with the particulate trap 14 oxidizes aportion of the regenerative agent to generate heat and elevate thetemperature of the particulate trap 14 each time that the ratio is at ahigher agent level. Indeed, the oxidation catalyst 19 oxidizesregenerative agent so as to generate heat for elevating the temperatureof the particulate trap 14 whenever there is oxygen and an amount ofregenerative agent at the catalyst 19 (i.e., not just when theregenerative agent is at a higher agent level).

The particulate trap 14 is partially regenerated with oxygen present inthe flow and with heat generated by the catalyst 19 each time that theratio is at a lower agent level. As such, each partial regenerationcycle includes commencing partial regeneration of the NOx trap 12 andinterrupting partial regeneration of the particulate trap 14 uponcommencement of partial regeneration of the NOx trap 12. Each partialregeneration cycle further includes commencing partial regeneration ofthe particulate trap 14 and interrupting partial regeneration of the NOxtrap 12 upon commencement of partial regeneration of the particulatetrap 14.

The regenerative agent thus serves as a NOx-reducing agent for reducingNOx at the NOx trap 12 and serves as an oxidizable agent to be oxidizedat the catalyst 19 to generate heat for regeneration of the particulatetrap 14. As such, the agent may take a variety of forms. For example,the agent may be a hydrocarbon fuel (e.g., diesel, gasoline, propane,alcohol, methanol), hydrogen (H₂), carbon monoxide (CO), and/or otherfuels. In such a case, the ratio of the oxygen content and theregenerative agent content of the flow may be the “lambda value” orcorresponding air-to-fuel ratio of the flow advanced to the emissionabatement device 16.

When the traps 12, 14 are separate components as in option 1 of FIG. 1,the particulate trap 14 may be positioned upstream from the NOx trap 12.In addition, the catalyst 19 may be positioned upstream from theparticulate trap 14 or integrated into the particulate trap 14.

When the traps 12, 14 are combined in an integrated device as in option2 of FIG. 1, the catalyst 19 may be a separate component upstream fromthe integrated device or integrated into the integrated device.

Carbon monoxide (CO) may be generated as a by-product of each partialregeneration of the particulate trap 14 (i.e., during each phaseinvolving lower levels of regenerative agent such as agent-lean phases).CO is useful as a reducing agent to reduce NOx in the NOx trap 12. Inaddition, each partial regeneration of the particulate trap 14 generatesheat which raises the temperature of the NOx trap 12 (e.g., to about600° C.). Such temperature elevation of the NOx trap 12 facilitatesdesulfation of the NOx trap 12 during phases involving higher levels ofregenerative agent (e.g., agent-rich phases).

Referring to FIG. 2, there is shown a graph illustrating oscillation ofthe ratio of the oxygen content and regenerative agent content of theflow over time. The ratio is shown in FIG. 2 as both the agent-to-oxygenratio (solid line) to highlight the regenerative agent content and asthe inverse oxygen-to-agent ratio (dashed line) to highlight the oxygencontent. As such, an increase in the agent-to-oxygen ratio represents anincrease in the regenerative agent content of the flow delivered to theemission abatement device 16. Conversely, an increase in theoxygen-to-agent ratio represents an increase in the oxygen content ofthe flow delivered to the emission abatement device 16.

Illustratively, the ratio waveform is generally sinusoidal. It is withinthe scope of this disclosure for the ratio waveform to be other thansinusoidal (e.g., a step waveform or near step waveform). Regardless ofthe particular shape of the ratio waveform, the ratio waveform has aplurality of adjacent peaks 20 and valleys 22, each adjacent peak andvalley producing one cycle. Such peaks 20 and valleys 22 in the ratiowaveform achieve oscillation of the ratio to alternately partiallyregenerate the NOx trap 12 and particulate trap 14 for the plurality ofcycles until completion of regeneration of the traps 12, 14.

Referring back to FIG. 1, the emission abatement device 16 is containedin an exhaust gas passageway 24 for conducting exhaust gas (“EG”)through the traps 12, 14. The exhaust gas is generated by an exhaust gassource such as an internal combustion engine 26 (e.g., diesel engine)fluidly coupled to the passageway 24. The ratio oscillator 18 isconfigured, for example, as an agent injection system that is fluidlycoupled to the passageway 24 and that oscillates injection ofregenerative agent into exhaust gas flowing through the passageway 24between higher and lower agent levels so as to alternately partiallyregenerate the NOx trap 12 and the particulate trap 14 for the pluralityof cycles. The regenerative agent delivered to the emission abatementdevice 16 is thus a combination of the injected regenerative agent andany regenerative agent already present in the exhaust gas [e.g.,unburned hydrocarbon fuel, hydrogen (H₂), carbon monoxide (CO)]. It iswithin the scope of this disclosure for the lower agent level to be zeroor non-zero.

As an agent injection system, the ratio oscillator 18 includes acontroller 27 electrically coupled to a flow control device 28 via anelectrical line 29 and electrically coupled to a pump 30 via anelectrical line 31. The controller 27 is configured to control operationof the pump 30 to cause regenerative agent to be pumped from an agentsupply 32 past the flow control device 28 and injected into the exhaustgas passageway 20. The controller 27 is configured to control operationof the flow control device 28 to cause the flow control device 28 tooscillate injection of the regenerative agent into the passageway 20between higher and lower agent levels, thereby oscillating the ratio ofthe oxygen content and regenerative agent content of the exhaust gasflow in the passageway 20 to the emission abatement device 16.

Exemplarily, the flow control device 28 is a valve. The valve may take avariety of configurations. For example, it may be a rotatable flappervalve. In other cases, it may be a solenoid valve movable between openedand closed positions in response to energization and de-energization ofthe solenoid valve.

The agent supply 32 may be a fuel supply to supply fuel. Moreparticularly, the agent supply 32 may be a hydrocarbon fuel supply tosupply hydrocarbon fuel, a hydrogen supply to supply to H₂, and/or a COsupply to supply CO. In the particular case where the engine 22 is adiesel engine onboard a vehicle, the supply 32 may be a diesel fuelsupply due to the ready availability of diesel fuel already onboard thevehicle.

It is within the scope of this disclosure for the ratio oscillator 18 tobe coupled to the engine 26 by a line 40 to inject the regenerativeagent into one or more cylinders of the engine 26 in addition to orinstead of injecting the regenerative agent into the exhaust gaspassageway 24. In particular, the ratio oscillator 18 may inject theregenerative agent into exhaust gas present in the cylinder(s) justbefore the exhaust gas is discharged from the cylinder(s). Theregenerative agent is thus discharged from the engine 26 with theexhaust gas into the exhaust gas passageway 24 for delivery to theemission abatement device 16.

It is further within the scope of this disclosure for the ratiooscillator 18 to oscillate injection of regenerative agent into exhaustgas of the engine 26 in response to at least one of a flow of airintroduced into the engine 26, an engine out lambda value measured by alambda sensor 42 electrically coupled to the controller 27 by anelectrical line 44, and an engine map 46 of the engine 26. The enginemap 46 may be integrated into the controller 27 or be separate from thecontroller 27 as part of some other device such as the engine controlunit. It is within the scope of this disclosure for the controller 27 tobe integrated into or be separate from the engine control unit.

While the concepts of the present disclosure have been illustrated anddescribed in detail in the drawings and foregoing description, suchillustration and description is to be considered as exemplary and notrestrictive in character, it being understood that only the illustrativeembodiments have been shown and described and that all changes andmodifications that come within the spirit of the disclosure are desiredto be protected.

There are a plurality of advantages of the concepts of the presentdisclosure arising from the various features of the systems describedherein. It will be noted that alternative embodiments of each of thesystems of the present disclosure may not include all of the featuresdescribed yet still benefit from at least some of the advantages of suchfeatures. Those of ordinary skill in the art may readily devise theirown implementations of a system that incorporate one or more of thefeatures of the present disclosure and fall within the spirit and scopeof the invention as defined by the appended claims.

1. A method, comprising the steps of: oscillating a ratio of the oxygencontent and regenerative agent content of a flow advanced to an emissionabatement device comprising a NOx trap and a particulate trap, andalternately partially regenerating the NOx trap and the particulate trapfor a plurality of cycles in response to the oscillating step.
 2. Themethod of claim 1, wherein: the oscillating step comprises operating avalve so as to oscillate injection of a hydrocarbon fuel into exhaustgas advanced to the emission abatement device, and the regenerating stepcomprises (i) partially regenerating the NOx trap with the injected fueland other regenerative agent present in the exhaust gas each time theratio is at a higher fuel level, (ii) generating heat each time theratio is at a higher fuel level, and (iii) partially regenerating theparticulate trap with oxygen present in the exhaust gas and with thegenerated heat each time the ratio is at a lower fuel level.
 3. Themethod of claim 1, wherein the oscillating step comprises oscillatingthe ratio of the oxygen content and regenerative agent content ofexhaust gas advanced to the emission abatement device.
 4. The method ofclaim 1, wherein the oscillating step comprises oscillating injection ofregenerative agent into exhaust gas advanced to the emission abatementdevice.
 5. The method of claim 4, wherein the injection oscillating stepcomprises operating a valve so as to oscillate injection of theregenerative agent into the flow of exhaust gas.
 6. The method of claim4, wherein the injection oscillating step comprises oscillatinginjection of a fuel into the exhaust gas.
 7. The method of claim 1,wherein: the oscillating step comprises oscillating the ratio betweenhigher and lower agent levels, and the regenerating step comprises (i)partially regenerating the NOx trap when the ratio is at a higher agentlevel and (ii) partially regenerating the particulate trap when theratio is at a lower agent level.
 8. The method of claim 7, wherein: theregenerating step further comprises generating heat when the ratio is ata higher agent level, and the step of partially regenerating theparticulate trap comprises partially regenerating the particulate trapwith the generated heat and oxygen present in the flow.
 9. The method ofclaim 1, wherein the regenerating step comprises (i) commencing partialregeneration of the NOx trap and interrupting partial regeneration ofthe particulate trap upon commencement of partial regeneration of theNOx trap and (ii) commencing partial regeneration of the particulatetrap and interrupting partial regeneration of the NOx trap uponcommencement of partial regeneration of the particulate trap.
 10. Anapparatus, comprising: a NOx trap and a particulate trap, an exhaust gaspassageway in which the NOx trap and the particulate trap arepositioned, and an agent injection system configured to oscillateinjection of a regenerative agent into the exhaust gas passagewaybetween higher and lower agent levels so as to alternately partiallyregenerate the NOx trap and the particulate trap for a plurality ofcycles.
 11. The apparatus of claim 10, wherein the agent injectionsystem comprises an agent supply, a flow control device positioned tocontrol flow of the agent from the agent supply to the exhaust gaspassageway, and a controller coupled to the flow control device to varyoperation thereof to oscillate injection of the regenerative agent. 12.The apparatus of claim 10, wherein the agent injection system comprisesa fuel supply to supply fuel as the injected regenerative agent.
 13. Theapparatus of claim 10, wherein the agent injection system comprises avalve operable to oscillate injection of the regenerative agent.
 14. Theapparatus of claim 13, wherein the agent injection system comprises acontroller coupled to the valve to vary operation of the valve tooscillate injection of the regenerative agent.
 15. An apparatus,comprising: an emission abatement device comprising a NOx trap and aparticulate trap, and a ratio oscillator configured to oscillate a ratioof the oxygen content and regenerative agent content of a flow advancedto the emission abatement device so as to alternately partiallyregenerate the NOx trap and the particulate trap for a plurality ofcycles.
 16. The apparatus of claim 15, wherein the ratio oscillator isconfigured to oscillate the ratio between higher and lower agent levelsso as to partially regenerate the NOx trap each time that the ratio isat a higher agent level and to partially regenerate the particulate trapeach time that the ratio is at a lower agent level.
 17. The apparatus ofclaim 16, wherein the emission abatement device comprises a catalystassociated with the particulate trap to elevate the temperature of theparticulate trap in the presence of oxygen and regenerative agent. 18.The apparatus of claim 15, wherein: the emission abatement device ispositioned in an exhaust gas passageway, and the ratio oscillatorcomprises a fuel supply to supply a fuel, a valve fluidly coupled to thefuel supply and fluidly coupled to the exhaust gas passageway at alocation upstream from the emission abatement device, and a controllercoupled to the valve to vary operation thereof to oscillate injection ofthe fuel into the exhaust gas passageway.
 19. The apparatus of claim 15,further comprising an engine fluidly coupled to the emission abatementdevice, wherein the ratio oscillator is configured to oscillateinjection of a regenerative agent into exhaust gas of the engine inresponse to at least one of a flow of air introduced into the engine,the lambda value of the exhaust gas, and a map of the engine.
 20. Theapparatus of claim 15, further comprising an engine fluidly coupled tothe emission abatement device, wherein the ratio oscillator is coupledto the engine to inject a fuel into the engine.